In a Long Term Evolution (LTE) Release 10 (Rel-10) system, various reference signals have been defined for downlink transmission, which mainly include Cell-specific Reference Signal (CRS), User Equipment (UE)-specific Reference Signal (UE-RS, also called as Demodulation-Reference Signal (DM-RS)) and Channel State Indication Reference Signal (CSI-RS). The CSI-RS is used to measure and estimate a downlink channel.
FIGS. 1a, 1b and 1c each shows a reference signal pattern of CSI-RS supporting by the LTE system. These reference signal patterns show resource positions of different reference signals, i.e., the positions of Resource Elements (REs) to which the different reference signals are mapped in a Physical Resource Block (PRB).
One reference signal is transmitted via each downlink antenna port, and 2-port, 4-port or 8-port CSI-RS may be configured. One PRB includes 20 groups of 2-port CSI-RS (as shown in FIG. 1a, each group of 2-port CSI-RS are mapped to a set of REs marked as 0 and 1), or 10 groups of 4-port CSI-RS (as shown in FIG. 1b, each group of 4-port CSI-RS are mapped to a set of REs marked as 0 to 3), or 5 groups of 8-port CSI-RS (as shown in FIG. 1c, each group of 8-port CSI-RS are mapped to a set of REs marked as 0 to 7). A numeral in each box in FIGS. 1a, 1b and 1c represents a port number. Every two ports are multiplexed in a code division manner on two adjacent REs. For example, in FIG. 1a, ports 0 and 1 are multiplexed on the set of REs marked as 0 and 1, in the form of (1, 1) and (1, −1). This multiplexing mode is represented as 2-bit Orthogonal Cover Code (OCC), i.e., OCC=2.
Based on the above, 12-port CSI-RS and 16-port CSI-RS have been introduced into Rel-13. The 12-port CSI-RS and the 16-port CSI-RS are both generated through port aggregation. In addition, in order to improve the power utilization, on the basis of OCC=2 in Rel-10, OCC=4 has also be introduced into Rel-13. In this regard, the 12-port CSI-RS is acquired through the aggregation of three groups of 4-port CSI-RS (OCC=2 or OCC=4). As shown in FIG. 2a, three groups of 4-port CSI-RS marked as A, B and C are aggregated into 12-port CSI-RS. 16-port CSI-RS are acquired through the aggregation of two groups of 8-port CSI-RS (OCC=2 or OCC=4). As shown in FIG. 2b, 8-port CSI-RS marked as A and B, and 8-port CSI-RS marked as C and D are aggregated into the 16-port CSI-RS. In FIGS. 2a and 2b, CSI-RSs marked as a same letter form one sub-group of OCC=4, and a Time Division Multiplexing (TDM) mode in conjunction with a Frequency Division Multiplexing (FDM) mode is adopted by each sub-group. Each group of 4-port CSI-RS are multiplexed on the four REs in each sub-group.
However, currently it is impossible for the LTE system to support transmission of the more-than-8-port CSI-RS, e.g., 16-port CSI-RS.